Page 300 - Clinical Anatomy

ECA5 7/18/06 6:50 PM Page 285

The larynx 285

strap muscles of the neck, the omohyoid, sternohyoid and thyrohyoid, find
attachment to it, only the sternothyroid failing to gain it.
The epiglottis is a leaf-shaped elastic cartilage lying behind the root of the
tongue. It is attached anteriorly to the body of the hyoid by the hyoepiglottic
ligament and below to the back of the thyroid cartilage by the thyroepiglottic
ligament immediately above the vocal cords. The sides of the epiglottis are
connected to the arytenoids by the aryepiglottic folds which run backwards
to form the margins of the entrance, or aditus, of the larynx.
The upper anterior surface of the epiglottis projects above the hyoid
bone; the epiglottic mucosa is reflected forward to the base of the tongue
and is raised up into a median glossoepiglottic fold and lateral pharyn-
goepiglottic folds. The depression on either side between these folds is
termed the vallecula.
The thyroid cartilage is shield-like, being made up of two lateral plates
meeting in the midline in the prominent ‘V’ of the ‘Adam’s apple’, the
laryngeal prominence, which is easily visible in the postpubertal male.
The cricoid is signet-ring shaped, deepest behind. It is the only complete
ring of cartilage throughout the respiratory tract. Inferiorly, it is attached to
the trachea by the cricotracheal membrane.
The arytenoids sit one on each side of the posterior ‘signet’ of the cricoid
cartilage.
In addition, there are two small nodules of cartilage at the inlet of the
larynx; the corniculate cartilage, a nodule lying at the apex of the arytenoid,
and the cuneiform cartilage, a flake of cartilage within the margin of the
aryepiglottic fold. These are of no functional importance. They are,
however, seen when the larynx is inspected through a laryngoscope (see
Fig. 207) and, to the uninitiated, might mimic pathological nodules.
The circothyroid membrane (cricovocal membrane) connects the thyroid,
cricoid and arytenoid cartilages. It is composed mainly of yellow elastic
tissue. Its upper edge is attached anteriorly to the posterior surface of the
thyroid cartilage and behind to the vocal process of the arytenoid. Between
these two structures, the upper edge of the membrane is thickened slightly
to form the vocal ligament. Anteriorly, the membrane thickens, as the
cricothyroid ligament; this is subcutaneous, easily felt and is used in emer-
gency cricothyroid puncture for laryngeal obstruction.
Passing forward from the arytenoid to the back of the thyroid cartilage,
just below the epiglottic attachment, are two folds of mucosa. The upper is
the vestibular fold, containing a small amount of fibrous tissue and forming
on each side the false vocal cord. The lower fold (the vocal fold or cord) con-
tains the vocal ligament (Fig. 206).
The mucosa is firmly adherent to the vocal ligament without there
being any intervening submucosa. This accounts for the pearly white, avas-
cular appearance of the vocal cords as seen on laryngoscopy. Oedema of the
larynx cannot involve the true cords since there is no submucous tissue in
which fluid can collect. The space between the vocal cords is the rima glot-
tidis. These folds demarcate the larynx into three zones:
1◊◊the supraglottic compartment (vestibule) above the false cords;
2◊◊the glottic compartment between the false and true cords;